The invention relates to a novel electrical or electronic component provided with a sealed encapsulation system. It also relates to the process allowing it to be produced.
The field of the invention therefore relates more particularly to components and microcomponents, also having electronic chips, but also to microsensors, microactuators, etc.
These microcomponents are conventionally deposited on a substrate of suitable nature, for example of the semiconductor (monocrystalline silicon, sapphire, etc.) type for electronic components. A number of electrically conducting tracks radiate from this microcomponent, towards the periphery of the substrate, so as to allow not only electrical supply to the component, if required, but also the processing and exploitation of the signals that it is called upon to generate, or even the control of the functions that it incorporates. Sometimes, a protective casing or cover is added to this component, suitable for preventing the problems inherently associated with impacts, with corrosion, with electromagnetic interference, etc., the said cover being attached, for example, by adhesive bonding. This cover may furthermore incorporate a window transparent to radiation to be detected by the said component or else a lens for focusing the said radiation onto the component.
Some of these microcomponents require for their operation to work under vacuum or in a controlled atmosphere (pressure, inert gas(es), etc.), or in a sealed manner with respect to the ambient atmosphere. Consequently, the aforementioned casing or cover is used so as to define a cavity above the said component, containing the suitable controlled atmosphere or the vacuum. The two technical concerns to be taken into consideration are therefore:
firstly, the hermeticity of the cover-component bond, intended to isolate the said component from the external agents, independently of the nature of the atmosphere then imprisoned in the volume thus defined;
secondly, the controlled nature of the atmosphere confined in the said volume, requiring that this atmosphere be distributed within this volume prior to sealing the cover onto the component.
Up to the present time, various techniques have been employed to thus allow the said electronic component to be encapsulated in a sealed manner. Among these, as described, for example, in the documents WO 95-17014 and GB-A-2,310,952, is the use of a cover or lid, which is aligned with the support provided with its electronic component and which is soldered around the entire periphery of the said support. This soldering or sealing conventionally produces a metal/metal junction typically involving a soldered joint made of indium or of a tin/lead alloy.
Conventionally, this technique is carried out in two steps: it consists in aligning the cover with respect to the component, both being within a suitable enclosure so as to provide a controlled atmosphere or, if this is not the case, a vacuum chamber, depending on the atmosphere desired, and then in sealing the said cover onto the component using technologies perfectly known to those skilled in the art.
It may be readily appreciated that, since a multiplicity of these operations has to be carried out, or a multicomponent support has to be employed, the equipment intended to carry out these operations becomes very complex and very expensive to operate, given that all these operations must be conducted within the enclosure for maintaining the controlled atmosphere or for maintaining the vacuum, as already mentioned.
Production of such microcomponents requires increasing use of techniques similar to those in microelectronics, the said components being fabricated in a collective manner. However, these microcomponents fulfil increasingly sophisticated and complex functions requiring a corresponding increase in the connection technology intended to allow them to be used.
This is because these microcomponents require a large number of electrical inputs and outputs so as to make it possible, on the one hand, for them to operate and, on the other hand, for their effects to be exploited. This number of inputs and outputs requires an equal number of electrically conducting tracks, which tracks fan out towards the periphery of the support, because of a corresponding number of connection pads around the outside, leading as it were to a considerable increase in the area occupied just by the connection system. Paradoxically, the advances made in microelectronics make it possible to reduce the active part of the component proper. In other words, a significant part of the high-performance, and therefore expensive, material used, namely the substrate bearing the component, is assigned for the sole purpose of receiving the connection tracks.
Consequently, it may be readily appreciated that collective fabrication loses its effectiveness and that, in some cases, the superfluity of connections no longer makes it possible for them to be made on a single level. In addition, when a welded casing is required, the connections must be protected from the solder bead by the use of an insulating layer, generally called a passivation layer.
In order to cope with this increase in connections, it has been proposed to produce the stack of several connection levels by separating the said levels by an insulating passivation layer. However, although this passivation technique makes it possible to solve the problem at the immediate level of the component itself, it cannot, of course, deal with the solder pads intended for making the external connections. Furthermore, although this passivation technique is relatively well controlled, it does have quite a number of deficiencies, such as leaks, short circuits, etc., which affect the efficiencies. Finally, and above all, it involves additional steps in the production of the microcomponents and furthermore generates a larger amount of scrap since each step is associated with a not insignificant scrap level, consequently affecting the overall production cost of such microcomponents.
It has also been proposed, still with the objective of coping with this increase in connections, to transfer at least some of these connections to the protective cover or casing. Thus, in document EP-A-0,609,062, the cover includes several conducting tracks produced on its external face and electrically connected to the electronic component located inside the volume defined by the support/cover assembly via conducting penetrations. These conducting penetrations extend into the thickness of the said cover and are solid, so as to ensure sealing within the aforementioned volume.
Thus, although it becomes possible to increase the amount of connections by this means, the problem associated with confining a controlled atmosphere or a vacuum within the volume defined by the support/cover assembly still remains, especially in terms of simplicity of the installation and given the manufacturing cost of the components thus produced. The drawbacks here are in fact the same as those associated with the cover used in document WO 95/17014.
The objective of the present invention is to solve these two main problems by proposing a device and a technology which are capable of significantly increasing the connection capacity of the component, especially for cases in which the severe environmental constraints dictate it, while still allowing effective encapsulation of the said component. Furthermore, the aim of the invention is, secondarily, to eliminate the need for passivation. However, in cases where there is a great need for connections, the invention makes it possible to provide both a standard level of connections on the substrate, within this passivated scenario, and a second level of connections on the casing.
This electrical or electronic component with sealed encapsulation comprises:
a support intended to house one or more electrical or electronic components from which electrically conducting tracks radiate towards the periphery of the said support; and
a protective and/or sealing casing attached to the said support and hermetically sealed with respect to the latter by means of a peripheral metal bead, the main part of the casing, intended to be placed opposite the said support, being provided with hollow conducting elements which pass right through the thickness of the said casing, from the (external) upper end of which elements electrically conducting metal tracks radiate towards the periphery of the casing, the internal lower end of which elements (with respect to the casing) being connected to at least one electrical connection track provided on the said support via a metal solder ball by hybridization.
In other words, one of the aspects of the invention consists in distributing all or some of the connections on the upper and therefore external face of the cover or casing, the transfer of these connections from the surface of the microcomponent to the casing being achieved by microballs, especially microballs made of indium or of tin/lead alloy, using the known technique of hybridization.
Hybridization by means of meltable microballs, generally made of indium or of tin/lead alloy, is well known for the production of collective electrical contacts for electrical components, whether the latter develop similar functions (stack of silicon circuits) or, on the contrary, greatly different functions (detection components on a read circuit, for example in the context of infrared detectors).
However, this technique has never been employed for the fitting of a protective casing provided with sufficient solid and sealed conducting penetrations when only hermeticity is desired in conjunction with the production of an upper level of connections on the casing, or of contact pads or plated through-holes, freeing an access for conveying the controlled atmosphere into the cavity thus defined, when, furthermore, it is simultaneously accompanied by the production of such a controlled atmosphere by the melting of a peripheral solder bead.
According to one advantageous characteristic of the invention, the metal solder balls are made of the same material as the peripheral solder bead.
According to another characteristic of the invention, the conducting elements provided through the main part of the casing consist exclusively of plated through-holes, the lower base of which is intended to come into intimate contact, for hermetic soldering, with the said balls or microballs after the peripheral solder bead has melted. This embodiment thus has the advantage of establishing, before the said casing is sealed onto the support, a controlled atmosphere or vacuum within the cavity defined by the casing and the support, the lower end of the said through-holes not being in contact with the solder balls before sealing.
According to the invention, the casing or cover may be equipped, depending on the case, with a transparent window or even with a radiation-focusing lens, or with any other member capable of fulfilling a simple technical function.
The invention also relates to the process for producing such a component.
This process consists:
firstly in placing, around a support having an electrical or electronic component provided with electrically conducting tracks which radiate towards its periphery, a continuous sealing bead made of a metal or a metal alloy having a low melting point, all or some of the said tracks stopping short of the said bead;
then, at the end of the said conducting tracks, in placing microballs which are made of a metallic material and have a diameter smaller than the diameter or the thickness of the said bead;
then in positioning, on the support thus produced, a casing or cover of suitable dimensions, the upper face of which, intended to be placed opposite the said support, is provided with hollow conducting elements which pass right through the said face and are located vertically above the said microballs, and is provided with conducting metal tracks extending from the upper end of the said conducting elements towards the periphery of the said cover, the said cover resting on the peripheral sealing bead; and
finally, in raising the temperature of the enclosure within which the assembly thus formed is positioned so as to melt the materials of which the peripheral sealing bead and the microballs are composed, causing, on the one hand, the lowering of the said cover towards the support and, as a corollary, its peripheral hermetic sealing to the said support suitable for ensuring that the internal volume thus defined is peripherally sealed with respect to the outside and, on the other hand, the soldering of the said microballs at the lower end of the conducting through-elements in such a way as to ensure that there is electrical continuity between the conducting tracks on the support and those on the cover or casing and that the volume thus defined is sealed.
Advantageously, the hollow conducting through-elements consist of plated through-holes and the temperature rise within the enclosure results in the melting and the hermetic soldering of each of the microballs within the said holes.
The manner in which the invention may be realized and the advantages which stem therefrom will be better appreciated from the illustrative embodiment which follows, given by way of non-limiting indication, supported by the appended figures.
FIG. 1 is an exploded perspective schematic illustration of the elements involved in the composition of the component according to the invention, prior to the sealing operation.
FIG. 2 is a schematic top view of the component according to the invention.
FIG. 3 is a cross-sectional view showing the preparation step prior to the soldering operation.
FIG. 4 is a similar view when the sealing operations have been completed.
FIG. 5 is a perspective schematic illustration of the casing/support assembly obtained after sealing.